We use Discord rather extensively but we don't have this problem. I don't think the issue is Discord itself (or for that matter any chat, be it IRC or Matrix) but the way it is used. I think it unfair to just blacklist a project just because it uses it.

We use Discord for team chat and conversations, the instant nature of a chat app suits this purpose far more than an async platform like a forum for us. This is either commonly known or transient info, not something we are interested in preserving. Long form conversations (like the status of our OS packaging) that require input over a long period goes into a forum topic.

We also use it for support for short form questions and help - anything more than a quick answer or "active" help then we recommend filling in an issue form or using the forum.

If a question comes up more than a few times then we make sure that it is documented - either in an FAQ or in the main documentation as it is clear that information isn't readily available or easy to find.

I'm not necessarily defending their use of Discord as I don't know exactly what they are doing but it does seem they don't have any alternative community areas. In contrast, yes we have a Discord but we also have a Lemmy community, a Subreddit (I'm honestly against keeping that one going but we would rather not shut out users from support), Mastodon and forum.

So no, it doesn't increase volunteer load in all cases, it is a valuable tool for us. Not that I'm wedded to Discord in particular (I'd honestly prefer to migrate it all to Matrix) but the idea of a chat platform for projects is not a bad thing by itself, it is how the project uses it.